fix: drop conv and campaign seq on account delete (#4256)

Conversation and campaign sequences persist in the database even after the related account is deleted. This PR adds an after_desttory callback on the account model that will delete the associated sequences.

Fixes: #4252

app/models/account.rb

@@ -79,6 +79,7 @@ class Account < ApplicationRecord
 
   before_validation :validate_limit_keys
   after_create_commit :notify_creation
+  after_destroy :remove_account_sequences
 
   def agents
     users.where(account_users: { role: :agent })
@@ -137,4 +138,9 @@ class Account < ApplicationRecord
   def validate_limit_keys
     # method overridden in enterprise module
   end
+
+  def remove_account_sequences
+    ActiveRecord::Base.connection.exec_query("drop sequence IF EXISTS camp_dpid_seq_#{id}")
+    ActiveRecord::Base.connection.exec_query("drop sequence IF EXISTS conv_dpid_seq_#{id}")
+  end
 end